NAME

       CheckDigits::M10_004 - compute check digits for 2aus5, EAN, ILN, ISBN13, NVE

SYNOPSIS

         use Algorithm::CheckDigits;

         $ean = CheckDigits('ean');

         if ($ean->is_valid('7622200004607')) {
               # do something
         }

         $cn = $ean->complete('762220000460');
         # $cn = '7622200004607'

         $cd = $ean->checkdigit('7622200004607');
         # $cd = '7'

         $bn = $ean->basenumber('7622200004607');
         # $bn = '762220000460'

DESCRIPTION

   ALGORITHM
       1.  Beginning right all numbers are weighted alternatively 1 and 3 (that is the check
           digit is weighted 1).

       2.  The sum of all products is computed.

       3.  The sum of step 3 ist taken modulo 10.

       4.  The check digit is the difference between 10 and the number from step 3.

       To validate the total of the digits of all numbers inclusive check digit taken modulo 10
       must be 0.

   METHODS
       is_valid($number)
           Returns true only if $number consists solely of digits, spaces and hyphen and the last
           digit is a valid check digit according to the algorithm given above.

           Returns false otherwise,

       complete($number)
           The check digit for $number is computed and concatenated to the end of $number.

           Returns the complete number with check digit or '' if $number does not consist solely
           of digits, spaces and hyphen.

       basenumber($number)
           Returns the basenumber of $number if $number has a valid check digit.

           Return '' otherwise.

       checkdigit($number)
           Returns the checkdigit of $number if $number has a valid check digit.

           Return '' otherwise.

   EXPORT
       None by default.

BUGS AND LIMITATIONS

       When invoked as "CheckDigits('isbn13')" the module checks whether the first three digits
       (the country code) are 978 or 979, the current (as of 2006) EAN country codes for books.
       If at any time other EAN country codes for ISBN-13 will be specified and the then
       responsible maintainer ignores this in the code, please send a friendly email.

AUTHOR

       Mathias Weidner, <mathias@weidner.in-bad-schmiedeberg.de>

SEE ALSO

       perl, CheckDigits, www.pruefziffernberechnung.de.